Problem: Emily is 4 times as old as Umaima and is also 18 years older than Umaima. How old is Umaima?
Explanation: We can use the given information to write down two equations that describe the ages of Emily and Umaima. Let Emily's current age be $e$ and Umaima's current age be $u$ $e = 4u$ $e = u + 18$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $u$ , and both of our equations have $e$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 =$ $4u$ $-$ $ (u + 18)$ which combines the information about $u$ from both of our original equations. Solving for $u$ , we get: $3 u = 18$ $u = 6$.